Oscillator Cylinder Pattern

[Sanjay F]

I have seen that engine too - very nice, bit of an eye-watering price and complete and not in need of attention; interesting mechanism if its a rotary valve, how can you tell?

[Jasonb]

Back to the question of spring pressure vs air/steam pressure.

The small oscillating engine I finished a couple of days ago was running at 2bar which is approx 30psi. I took the spring off and stood it on some scales then pushed down on the spring until it compressed to the same installed length as it was on the engine. It about about 1KG or 2.2lbs this for a 6mm OD spring of 0.8mm wire diameter.

[vtsteam]

Thanks guys!

CI, I'm really glad I decided on a boring table when I made the lathe. The boring carriage is also something I made, I am including some photos below to show that better. It's just some pieces of angle iron and flat bar stock welded together. The bottom has adjusters (the hex headed bolts) for leveling and height adjustment, and socket head cap screws near them are the hold downs that bolt it to the table. To adjust it I use an open end wrench and an Allen key. It seems to work well.

In boring news today, the 1-1/4" dia boring bar I started with was overkill -- really made for a 2-1/4" by 6" long cylinder I once machined. The big problem for this smaller cylinder was that there was no way to measure the bore as it progressed, because I couldn't fit inside calipers in the small gap beside the boring bar. So I switched tactics to using an overhung 5/8" bar I had, held in the an MT2 collet in the lathe spindle.

This unfortunately did chatter some in moderate cuts, so I had to go in small increments, which took a long time. I really should make a 3/4" bar with a morse taper on the end -- that would have been ideal. But we made do with what we had for the moment.

The way I set the cutter was with an old gauge I had once made when building my original Gingery lathe. Very simple device made from strap, threaded rod, and some square keystock. It hooks onto the boring bar, and then you bring the adjustable screw down to touch a feeler gage for the depth you want to increase your cut. Remove the feeler, and then loosen the cutter's retaining screw, and move the cutter in to touch the screw. Then retighten the retaining screw.

This all works remarkably well unless you get impatient like I did at the last 4 thou to finish. I reset the cutter 2 thou, but finished the bore at 1.503".  I should have made multiple passes at the last setting rather than adding one more, because of the springback in the 5/8" bar. That's what I used to do with the 5/8 bar. Been a long time.

And I also stopped early because I was over, so the bore wasn't as smooth as it would have been If I' done those last springback passes. So, once done I honed the cylinder and I finally finished at 1.505" Walk of shame.....

Anyway, bore is smooth and consistent now. I'm really happy to move on, because everything else is now determined, size-wise. The bore fixes the dimensions of other parts, so I can do a lot more.

Progressing Well but never too late to go with a vertical, this popped up last night and I thought of your cylinder. I think it mast have a form or rocking or rotary valve on the trunion but a nice looking engine.

That is VERY very tempting, Jason. What a great looking engine! I would love to try making those castings. But for now I think I'll stick with the horizontal, just because I've always wanted to build one. But I might circle back to that vertical some day!

[vtsteam]

Back to the question of spring pressure vs air/steam pressure.

The small oscillating engine I finished a couple of days ago was running at 2bar which is approx 30psi. I took the spring off and stood it on some scales then pushed down on the spring until it compressed to the same installed length as it was on the engine. It about about 1KG or 2.2lbs this for a 6mm OD spring of 0.8mm wire diameter.

Jason, thanks greatly! Can I ask if that has channels around the standards, or a manifold and two sets of holes. I was thinking about making channels, but thought that might increase the spring load.

[Jasonb]

Have a look at the "is there time" thread where I have started to show the build, you can see the port face.

[vtsteam]

Back to the question of spring pressure vs air/steam pressure.

The small oscillating engine I finished a couple of days ago was running at 2bar which is approx 30psi. I took the spring off and stood it on some scales then pushed down on the spring until it compressed to the same installed length as it was on the engine. It about about 1KG or 2.2lbs this for a 6mm OD spring of 0.8mm wire diameter.

OK, thanks, now I realize which small engine you were talking about here -- I thought it was the one whose cylinder you illustrated earlier.

Well, the Willy engine has a very small contact area surrounding the steam port. The necessary spring pressure (as I am imagining it) would be proportionate to both the steam pressure, and the enclosed contact area surrounding the steam ports.

I guess the amount of spring I'll need will be very dependent on the shape of the trunnion standard's face. I had originally thought it would look something like the below image (source, Julius' Muncaster dwg). The channels are a way of avoiding an external manifold. But that design might, I think, pressurize the whole contact face, which on my engine, is ~ 3 square inches. 50 psi in that interface would have serious lift, unless there's something at work here that I don't understand.

Now a way around that would be to run closed passages inside the trunnion, as you did in Willy, not face channels. And also to open a large amount of the contact space to atmosphere, as you also did with your relief cut.

   

[Jasonb]

The horizontal one has drilled and plugged passages but uses the screw on the other trunion to hold the cylinder against the port face not a spring







I have similar springs on the Vee twin I did a couple of weeks ago, similar drilled passages but no relief of the port face. They are closed up by a similar amount to the single.



Another one with plugged drilled passages and unrelieved portface





If you are worried about the half moon shaped ports as well a sthe drill and plug method you can also make the port with a separate face. Mill or cast the half moons into the trunion bracket then fit a separate disc to the front say 1/16" thick that just has the four holes/slots. If you machined a recess in the trunion blocks face say 0.055" deep then it would hardly show on the outside that you have a two piece assembly.

Similar idea to this where I wante dto get gas all around

[vtsteam]

Thanks Jason, that's a wealth of helpful photos. I was also thinking about the plate and channel idea, and it might have an advantage in that you could experiment with timing by how you milled the ports. It would be easy to change the plates to a slightly different configuration from the starting symmetrical timing. I don't know if I'll actually do that, but I might when I get to that stage.

I do kinda like the screw instead of spring loaded trunnion, even though CI was mentioning the change in clearance from heating up. I think if it's a stationary work engine running at steady speed it could be okay if there was a little more clearance when starting than when running. I guess you could add a spring if you didn't like the screw method after trying out anyway. Not a big change.

Okay, well enough thought experiment, and back into the shop. I'm excited to have the bore fixed now so I know what to do re. the covers, piston, rod, rings etc. And I am thinking in the back of my mind about the flywheel pattern.

Also one other possible project maybe first today -- I have an unused Atlas horizontal milling machine in storage. If I can somehow fit it into my very tiny ( 6' x 8') shop by moving some other stuff out of there, that would make a huge difference. I think there might just be space, but I have to measure carefully and think about it...

Thank you again for those photos and suggestions.

Later:
There was just enough room in the shop after moving the lathe, removing to storage a heavy cast iron surface plate that I rarely use, and shifting a lot of other things around.

I disassembled the Atlas horizontal mill to make carrying it easier -- it's about 200 lbs. Moved to it the shop, and then reassembled it this evening. The vertical lift is a little tight, so I'm going to disassemble the screw to check it and also check the gib for burrs, but otherwise the mill table works easily, and the motor, back gear and pulleys/belts are in good condition and run well together.

Shop is presently disorganized with all the moved tools, stock, and odds and ends in piles on the benches, but I'm hoping to have everything reorganized tomorrow. This is going to make a big difference!

[vtsteam]

It has taken awhile to get the shop back in working order after moving the horizontal mill in. But today I did a little work on the steam engine, even though things aren't fully organized. I just wanted to see some progress on it.

So I turned the spigots down to cylinder bore size on both end caps, and reduced their depth to .050". Fit was good.

Then I drilled the front cap 19/64" and opened that out with a 0.3135" reamer to fit the intended 5/16" connecting rod.

For the bottom end cap I used a home forged 1/4" dia. boring bar to relieve a 0.70" recess on the inside spigot, to provide clearance for the piston retaining nut.

[PaulR]

 

[vtsteam]

Thanks Paul! 

I did a little shaping today of the cylinder covers. I can't really use a form tool on my small lathe without chatter, so I had to etch-a-sketch X and Y ball handles. I also couldn't get too close to the chuck because of the inside jaws and my style of toolholder. But, I'm happy with what I was able to carve anyway, considering.

This cast is really nice stuff to work with.

I also drilled and threaded the front cover to accept a packing screw.

[CI]

Nice looking castings !
I have to agree, gray iron castings are great to work with.
My favorite material by far.
 
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[Jasonb]

Making good progress and good to see you have a decent length to the cylinder cover to guide the piston rod.

Yes Cast Iron can be very nice to machine but it can also be one of the worst if you get a poor casting that is chilled and/or has voids which yours don't have. Even fault free some castings are nicer than others depending on the grade of iron with some being like machining a pencil lead and others quite hard and grainy

[PaulR]

I also drilled and threaded the front cover to accept a packing screw.

Will you be using an o-ring, yarn or something else (I seem to recall some people even use rolled up PTFE?) and have you flattened the bottom of the hole or leaving it as drilled?

Nice job on the blending 

[CI]

Yes Cast Iron can be very nice to machine but it can also be one of the worst if you get a poor casting that is chilled and/or has voids which yours don't have. Even fault free some castings are nicer than others depending on the grade of iron with some being like machining a pencil lead and others quite hard and grainy

The beauty of making one's own iron castings is that the quality can be controlled closely, and consistently.
I have heard mixed stories about whether rotor iron is good for making engine castings, but I know of two folks who use them (one is VT), and they are having good success with that material.  My buddy anneals his castings made from rotors, and that is also an option, but I don't think that is something that is always necessary, as we see from VT's work.

Adding a somewhat exact amount of ferrosilicon is pretty critical when you get into thin castings.
Too much ferro and you get excessive shrinkage and hot tears.
The ferro seems to thin out the melt, and make it easier to final skim.
And of course getting a good skim before you pour is critical, else you are going to have random slag inclusions.

I use electric motor end bells, and those have worked consistently well, but it is good to see other materials that are useful, especially brake rotors, since they are so readily available.

It is really not difficult to get consistent high quality gray iron castings, if one pays attention to detail.
I have seen some break open a mold shortly after casting, and that is a bad idea with iron, and can lead to hard spots.
Iron castings should remain in the mold overnight, so that they can cool as slowly as possible.

Edit:
I have heard tales of foundries working in the hobby stuff at the end of a production run, and I would guess that the melt may be on the cold side, and the emphasis on quality may be zero.  I am not aware of any commerical foundry that is going to make much if any money dealing with casting kits for model engines.  I think commercial foundries are doing the kit folks a favor by even attempting to make limited production kit castings.
The Lone Star Ball Hopper Monitor iron castings I purchased from Maury were the best I have ever seen.
I purchased some Cretors replica iron castings, and some of them were full of blow holes and/or slag inclusions.
If the cores are not vented out the top of the cope, you can get blowholes in the castings; another thing that has to be watched.

My two cents are that if quality gray iron castings can be made in a backyard setting by multiple people (I know of six or more hobby folks who can make quality iron castings on any given day), then anyone selling substandard gray iron castings is not really putting forth much effort as far as quality.

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